(1) Field of the Invention
The present invention relates to an amorphous lithium fluoaluminate and a solid electrolyte including this amorphous substance. More particularly, the present invention relates to an amorphous substance and solid electrolyte for use in the production of electrochromic display devices and lithium batteries.
(2) Description of the Prior Art
In order to make an all solid state electrochromic display device or the like, it is necessary to use a solid substance which has a lithium ion conductivity .sigma..sub.25 of at least 1.times.10.sup.-6 (.OMEGA.-cm).sup.-1 at room temperature (25.degree. C.) and is stable in air and which can easily be formed into a solid film having a thickness of 1 to 10 .mu.m. As the substance satisfying these requirements, there have been proposed and examined Li.sub.x Na.sub.1-x /.beta.-alumina and Li.sub.3 N as disclosed in Japanese Patent Application Laid-Open Specification No. 43505/80. However, the former substance is defective in that formation of a film is difficult, and the latter substance is defective in that it is not stable in air. In addition, films of RbAg.sub.4 I.sub.5, LiF, MgF.sub.2 and Cr.sub.2 O.sub.3 have been proposed. However, these films are defective in that the time required for coloration and bleaching is very long (longer than 1 minute), they are significantly influenced by the atmosphere, the reproducibility is poor, they have no memory action and the life is short.